Combustion of carbonaceous solids



March 2, 1965 F. M. STEPHENS, JR. arm. 3,171,369

COMBUSTIQN 0F CARBONACEOUS SOLIDS Filed Dec. 28, 1962 3 Sheets-Sheet 1Combustion Gass '.Z 2 so 2 g 70- b g 60- p 3 somvmons 8 4 r l l FRANK. MSTEPHENS, JR.

l ooo' I200 I400 I000 mm 2000 2200 WILLIAM TEMPERATURQF I M. sopnaaaesn:

ATTORNEY March 1965 F. M. STEPHENS, JR.. ETAL 3,171,359

COMBUSTION OF CARBONACEOUS SOLIDS Filed Dec. 28, 1962 3 Sheets-Sheet 27.0 t 0.0 r u 5.0 U Q u STABLE (L FLUIDIZATION H so u E h. E, 20 o. 3UNSTABLE 0 Le FLUIDIZATION 0 I900 I950 2000 2050 2:00 2l50 BEDTEMPERATURE, F

O m D 83A @2 1 5 f 2 d] 75 m S I 2 9 2? Ld 50' a v POUNDS-BED G SCFMINVENTORS FRANK M. STEPHENS, JR. WILLIAM M. GOLDBERGER ATTORNEY March1965 F. M. STEPHENS, Jli. ETAL 3,171,359

COMBUSTION OF CARBONACEOUS SOLIDS Filed Dec. 28, 1962 3 Sheets-Sheet 3Combustion Gases Ash Removal IN VENTORS FRANK M. STEPHENS, JR.

WILLIAM M. GOLDBERGER A T TORNEY United States Patent The presentinvention relates to a process of burning carbonaceous fuels and isparticularly related to the burning of carbonaceous solids by means offluidized solid process to produce hot, pressurized and dust-free gassuitable as a working fluid for gas turbines.

The use of coal for industrial power generation has receivedconsiderable commercial consideration in recent years. Most industrialplants use lump coal on mechanically operated grates and stokers, butsome burn coal in powdered or pulverized form. Grate-type burners do nothave as high a thermal efficiency and are more costly to operate thanpowdered coal burners. Burners for pulverized coal are more flexible andcan handle coals having widely different characteristics including theeasily fused or caking coals which are troublesome when burned ongrates. However, a serious disadvantage of pulverized coal burners inthe past has been the fact that finely divided ash (hereafter referredto as fly-ash), which is produced during the combustion process, iscarried away from the burner with the exhaust gas. The ash materials inthe gas are erosive and prevent the use of the gas in open-cycleturbines. Also, the ash-containing gas cannot be used efficiently as aheat exchange medium because the ash materials deposit on the interiorsur-' faces of the heat exchanger and reduce its heat transferability.Furthermore, the coal burning efficiencies of these burners are usuallylowered due to the fact that some carbon particles become surrounded bythe ash materials in the burner and are carried away by the combustiongas without undergoing complete combustion. Fly-ash materials in the gasare also undesirable from the standpoint of air pollution.

Auxiliary gas cleaning equipment such as cyclones have been employed butcomplete dependence thereon to remove suspended solids from the gas hasnot proved economically practical. The major difficulty is that the ashparticles entrained in the combustion gas are extremely small anddifficult to remove unless a plurality of gas cleaning equipment areemployed. To maintain a competitive position with other combustionprocesses using more convenient fuels, such as natural gas or fuel oil,coal-burning devices must provide for continuous operation with aminimum of labor or auxiliary mechanical equipment.

Accordingly this invention contemplates burning carbonaceous solids bymeans of a fluidized solids process to produce a hot, pressurized gaswhich is essentially completely dust-free. By the term dust-free it ismeant that the gas is essentially free from solid particles smaller thanabout 10 microns. These solid particles are extremely difiicult toremove by means of ordinary gas cleaning equipment, such as a cyclone.The gas, however, may contain solid particles larger than about 10microns, but these particles are readily removable by ordinarygascleaning equipment. A minor amount of solid particles of less than 10microns in size may be present in the gas, but their amount andconcentration is too low to cause erosion of the turbine blades orfouling of the interior surfaces of heat exchangers. This invention isaccordingly directed to burning carbonaceous solid particles with oxygenor air, in a combustion zone, under such operative conditions that thecarbonaceous solid particles burn substantially instantly as they areintroduced into the combustion zone. The temperature in the combustionzone is maintained at or slightly below tthe temperature of incipientfusion of the ash produced during the combustion reaction. Thus, the ashparticles soften, become tacky, stick together upon collision with otherash particles and agglomerate into larger particles which are eventuallywithdrawn from the combustion zone. Since, as was previously mentioned,the carbon particles burn rapidly and instantly as they enter thecombustion zone, the agglomerated ash which is withdrawn from thecombustion zone is essentially completely carbon-free. This permitsoperation at nearly percent combustion efiiciency since all thecarbonaceous solids feed can be burned with essentially no carbon lossesfrom the combustion zone. For example, ignition tests made on theseagglomerated ash particles when burning a bituminous coal at about 1975F. showed that the carbon level of the bed, determined as the percentloss on ignition was 0.70 percent. At 2100 F., however, the carbon levelwas found to be 0.55 percent. Similar results were found when burningsub-bituminous coal. The rapid burning of the carbonaceous solidparticles releases enormous quantities of heat which can be recoveredand utilized as will hereinafter be described. The combustion gaseswhich are thus produced are essentially completely free from fly-ash andfine suspended solids.

The novel process will be more clearly understood with reference to theattached drawings wherein:

FIGURE 1 is a schematic flow diagram of a process of burningcarbonaceous solids in a fluidized combustion zone.

FIGURE 2 is a plot of combustion efficiency as a function of bedtemperature in the combustion zone for one type of carbonaceous solidmaterials, i.e., powerhouse coal.

FIGURE 3 is a plot of superficial gas velocity versus bed temperature inthe combustion zone using powerhouse coal.

FIGURE 4 is a curve representing the relationship between percent ashremoved in the fluid-bed and W/ G, wherein W is the bed weight in poundsper square foot of cross-sectional area of the bed and G is the gas ratein standard cubic feet per minute per square foot of bed area, usingpowerhouse coal.

FIGURE 5 is a schematic flow diagram of a process of burningcarbonaceous solids in a combustion zone, operating in conjunction withgasification of carbonaceous solids in a gasification zone.

Referring to FIGURE 1, coal particles 1 are fed from a storage vessel 3through a metering valve 5 and feed pipe 7. Air is supplied from an airsupply source (not shown) into feed pipe 7 to carry coal particles 1into combustion zone 9. Air is employed both for fiuidizing and forburning said coal particles. Combustion zone 9 is provided with anoverhead line 11 to remove the combustion gases, discharge pipe 13 andmeter valve 15 for the withdrawal and metering of the solids from saidzone 9. Make-up coal may be introduced into the combustion zone viamake-up line 17, if necessary. The make-up coal particles are preferablyintroduced at a point below the surface of the bed to avoid elutriation.Other auxiliary equipment not shown in the drawing may form part of theapparatus employed in carrying out the novel process. For example, thecombustion gases may pass through a cyclone to insure complete removalof solid particles from the gas, if necessary.

The operation of this invention can be illustrated using pulverized coalas the carbonaceous solids feed to the combustion zone. However, othercarbonaceous sol-ids such as, for example, coke, slack, anthracite,asphalt, pitch, etc., or ash-containing liquid carbonaceous fuels suchas liquid asphalt, liquid petroleum residues, fuel oils, gas oils, etc.can be also employed with efiicacious results.

period of about several .hours,: the .bed temperature in: thecombustion. zone reaches the incipient'fusion tem@ perature of the ashmaterials. produced during the com- Cit bustion:reaction, causing theashiparticles to become tacky and agglomerate upon collisioniwith otherparticlesin the bed.- j

The temperature in the combustion zone can be con trolled by providing.saidizone. with. external cooling coils or a cooling jacket, or byadjusting the coal feed rate, or oxygen or air rate to the combustionzone. A particularly advantageous method of controlling thebedtemperature in the combustion zone can be accomplished by feedingwater slurry of coal, or by introducting water separately into-thecombustion zone by means of'line 17a. Water thus vaporizes in thecombustion zone, absorbing large quantities of heat (heat ofvaporization) which serves to control the temperature in the combustionzone. The quantity of water which is necessary to achieve the desireddegree of temperature control may, of course, bedetermined by thoseskilled in the art. Coal slurry feeding is particularly advantageouseconomically in commercial operations as the coal is often available inslurry form andcan therefore be pumped directly into the combustion zonewithout the necessity of drying and storing the coal.

Although not necessarily limited to the following mechanisms, theagglomeration of fly ash may occur in the following manner; As the coalparticles enter the fluidized combustion zone, they quickly reach theirig nition temperature and begin to burn. Combustion is rapid because thedispersed coal particles in the fluilized state present a large surfacearea for the combustion reaction. In addition the high rate ofagitationwithin the bed reduces the resistance-to heat and mass transferand permits rapid burning.- As the coal particles burn, localizedtemperatureswithin the particles exceed the ash softening temperatureand the ash contained in the coal particles becomes sticky. The burningcoal particles, upon contact with the bed particles containing thesoftened ash, adherethereto and continue to burn. In this mannercombustion proceeds and, at the same time, the flyashmaterials areremoved by agglomeration with the burning bed particles. The bedparticles in the combustion zone also agglomerate by another yet similarmechanism. Many of these bed particles have adhering on their surfacesthe burning coal particles just described. These particles" presentsticky exterior surfaces which are effective for collecting the fiy-ashmaterials from the combustion gases. In this manner fly-ash can beremoved from the combustion gases even though the ash itself is belowits incipient fusion temperature. A third mechanism bywhich'fiy-ashmaterials are removed from the combustion zone is asfollows: Many of the bed particles become partially'coated'with thesoftened and sticky ash materials, and will agglomerate upon collisionwith eachother.

At temperatures considerably below the incipient fusion temperature of'the'ash, the agglomeration and re-' :moval. of fly-ash is predominantlyby the first of the foregoing mechanisms. Thus, some fly-ash is removedeven at fluidized-bed temperatures far below the incipient fusiontemperature of the ash'materials, but the relative quantity of fly-ashremoved in this manner is usually very small. As the bed temperature israised, the flyash. materials are agglomerated and removed from thecombustion gases by a combinationof the first two mech anismshereinbefore described. The ash collection efficiency increases withincreased bed temperatures as will hereinafter be discussed. As the bedtemperature is further raised so that itis slightly below the incipientfusion temperature of the .ash. materials, agglomeration by thethirdrnechanism begins'to occur.-.

It should be 'empha'siz'ed' lthat the carbon particles quickly reachtheir ignition temperature and burn almost instantly as they areintroduced into the combustion zone. Thus, carbon particles are presentin the combustion zone for an extremely shortresidence time and areconverted to combustionproductswithout the danger of elutriation. Theinstantaneous and complete burning of the carbon particles thereforpermit operation at near ly 100 percent combustioneificiency sincetheentire carbon feed can be rapidly burned with substantially no carbonlosses from'thecombustion zone.

Theefficiency of the combustion reaction depends upon the'bedtemperature and the particle sizes of the 'coal. Since, as it waspreviously pointed'out, the coal particles burn almost instantly as theyare introduced into the combustion zone-extremely small coal particlescan be fed into the combustion zone without the danger of elutriationtherefrom. The smaller the particles, the greater the area available forcombustion, hence the more rapid and efiicient the combustion reaction.Coal particles of the order of less than about 1 micron can besatisfactorily employed for-the combustion reaction herein without thedanger of elutriation. The'relationship between combustion efficiencyand bed temperature is shown by the plot in FIGURE 2 for powerhousecoal. Efficiencies upwards of 90'percentior' better were obtained forbed temperatures of the order of about 1550 F. and higher, and anefliciency of nearly '100 percent was obtained at a bed temperature ofabout 1950" F. Similar plots can be'prepared to determine the optimumbed temperature corresponding to a desired combustion efficiency, orvice versa, for othercarbonaceous solids.

It should also be pointed out that there is a practical upper limit oftemperature. beyond which the bed cannot be maintained in fluidizedconditions. This temperature is the incipient fusion temperature oftheash materials producedduringtthe combustion reaction. At temperaturesabove the incipient fusion temperature, the agglomerated ash particlestend to fuse together, therefore causing the bed'to d'efluidize andcollapse. The incipient fusion temperature of the ash, of course, variesdepending upon the composition thereof, and is therefore different fordifferent carbonaceous solids.

The tendency'of'the bed to defluidize has been found to be directlyrelated to the adhesive forces on the surface of the bed particles andon the surface area available for particle contact. Adhesion ofparticles is also inversely proportional to the particle momentum. Asthe temperature is raised, the adhesive characteristics of the surfaceof the particles are increased and the agglomerating action is thereforeenhanced. However, the increased adhesiveness tends .to increase thedefluidization tendency of the bed. This phenomenon can be compensatedfor by increasing the. velocity ofthe fluidizing gas which tends'toincrease the momentum of the fluidized particles, hence decreasing the.tendency toward defiuidization.

The relationship between the gas velocity in the combustion 'zoneto thebed temperature, other. conditions being constant, is illustratedbythecurve in FIGURE 3. for a-particular type of coal,.i.e., powerhouse coal.The unshaded area above the curve indicates the area of stable fluid-bedoperation whereas the area below the curve indicatesthe area of unstablefluid-bed operation. Thus, at a temperature of, say, about 2000 F., thevelocity required for stable fiuidizationis determined by projecting avertical line from the abscissa corresponding to 2000" F. in FIGURE 3,and determining .the point of intersection of said line with the curve(corresponding to an-ordinate of about 1.4feet per second). The velocityof the fiuidizing gas is then chosen at slightly above the value of thevelocity so determined to insure operation within the area of stablefiuidization.

The collection efliciency of fly-ash particles is also related to theconditions of operation in the combustion zone. Although some fly-ash iscollected on the bed particles at all bed temperatures above theignition temperature of the coal particles, collection efliciency isbest when the bed temperature approaches the incipient fusiontemperature of the ash produced during the combustion process. Thecollection efliciency of fly-ash is dependent on such variables asbed-depth, fluid-bed density, the velocity of the fiuidizing gas and thebed temperatures. FIGURE 4 illustrates the relationship between percentash removal from the fluidized bed with W/ G as hereinbefore described.FIGURE 4 was prepared for a particular type coal, i.e., powerhouse coalof certain particle size, at three diflerent temperatures. It will benoticed from FIGURE 4 that the collection efficiency at a bedtemperature of, say 2050" F. is increased by increasing W or bydecreasing G. Thus, the collection efficiency at a given bedtemperature, and for a certain type and size coal, increases withincrease in bed depth and bed density and is lowered by higherfiuidizing velocities. The effect of the velocity of the fiuidizingmedium on the collection efiiciency, however, is less pronounced thanthe effect of bed depth and bed density. It should also be pointed outthat the collection efiiciency is not particularly effected by changesin coal feed rates to the combustion zone. In some studies, for example,the coal feed rate was increased by a factor of about 29 percent withoutnoticeable change in collection efiiciency, the bed depth and bedtemperature being constant.

Any oxygen-containing gas, preferably air, can be employed to fluidizethe bed in the combustion zone and to support the combustion ofcarbonaceous solid particles. Since the bed in the combustion zoneconsists mainly of agglomerated ash particles, relatively highvelocities of air can be employed through the combustion zone, ifdesired.

The pressure in the combustion zone can be atmosphenic orsuperatmospheric. Since the combustion gases are extremely useful asworking fluids for driving gas turbines, from the standpoint of energyrecovery in the turbine it is desirable to employ a pressurized gastherein. The combustion zone is, therefore, preferably maintained atsuperatmospheric pressures, most preferably in the range of from about20 p.s.i.g. to about 150 p.s.i.g. Accordingly, the fiuidizing medium(air) must be compressed prior to its introduction into the combustionzone.

The dust loading of the combustion gas which is produced by the processof this invention is extremely low, of the order of about 5 grains per100 cubic feet of the combustion gases or less. The extremely low dustloading of gas is related to the conditions maintained in the combustionzone.

The agglomerated ash particles which are withdrawn from the combustionzone are extremely valuable as high level heat exchange media. Forexample, they can be used to supply the heat of reaction to endothermicprocesses. In addition to serving as high level heat source, thewithdrawal of the agglomerated ash particles serves to control thetemperature in the combustion zone. Furthermore, the Withdrawal ofoversized agglomerated ash particles is necessary to maintain the bedfluidized throughout the entire operation. One particularly advantageousapplication of these hot agglomerated ash particles is to supply heatfor the gasification of carbonaceous solids as illustrated and describedin details in FIGURE 5.

Referring now to FIGURE 5, there are shown two interconnected fiuidizingzones, one, a combustion zone 9, and the other, a gasification zone 19.Like numerals in FIGURES 1 and 5 indicate like parts. The operation ofthe combustion zone is essentially as described in connection with thedetailed description of FIGURE 1. Coal particles from storage vessel 21are conveyed through feed line 23 and metering valve 25 intogasification zone 19. The coal particles can fall into gasification zone19 either by gravity or conveyed by some inert gas or by the fluidizingmedium itself. The fiuidizing medium in gasification zone 19 is usuallysteam, which is also the gasifying agent employed for the gasificationreaction. Steam is introduced into gasification zone 19 via conduit 27.The hot agglomerated ash from combustion zone 9 enters gasification zone19 through discharge line 13. It should be pointed out that thetemperature in the combustion zone is usually considerably higher thanthe temperature in the gasification zone. In addition, the sizes of theagglomerated ash from the combustion zone are preferably considerably:larger than the sizes of the coal particles in the gasification zone.Hence, the agglomerated ash particles progress downward in thegasification zone and after transferring their sensible heat to thereactants in the gasification zone they are withdrawn via line 29 andmay be metered through meter valve 31 if desired. Gasification zone 19may also be provided with another discharge line 33 to permit withdrawalof ash-like materials therefrom and to maintain a balanceofnon-combustibles within the system. Some of the agglomerated ashmaterials is withdrawn via lines 35, metered through meter valve 37 andrecycled by means of a carrier gas, such as air, through line 39 tocombustion zone 9. Product gases from gasification zone 19 are moved byline 41 and may be introduced into a cyclone or any other gas cleaningequipment (not shown) if necessary.

It should be pointed out that the velocity of the fluidizing medium inthe gasification zone is considerably lower than the Velocity requiredto maintain the agglomerated ash particles in fluidized condition.Consequently, it is possible to gasify the coal particles in thegasification zone under fluidized conditions and at the same timeutilize the sensible heat of the descending agglomerated ash particlesfrom the combustion zone.

The apparatus employed in the novel process can be constructed ofmaterials ordinarily employed for hightemperature fluid-bed operations.For example, the combustion zone may be lined with refractory materialscapable of withstanding the high temperatures and the erosive action ofthe fluidized bed.

Many modifications and revisions can be made both with regard to theapparatus employed in the novel process and in the details of operationwithout substantial departure from the scope of this invention. Also,the novel process is flexible and can be used with coals having Widelydifferent characteristics, and with other carbonaceous solids such ascoke, slack, anthracite, pitches, asphalts, etc.

Studies were made using a bituminous coal and a subbituminous coal. Thebituminous coal has a high heating value but is readily fusible andtroublesome to burn on grates. The sub-bituminous coal is noncaking,contains considerable moisture and volatiles, and has a low heatingvalue. The studies were made in a 6-inch diameter fluidized coal burnerin the manner hereinbefore described in connection with FIGURE 1 and thedetailed description of the operation of the novel process. The resultsare summarized in Table 1 below.

Table 1 Type of Coal Bitumi- Sub-bitunous minous Temperature of FludizcdBed, F 2, 050 2, 050 Bed Weight, lb 45 45 Goal Rate, lb./hr 7.00 8. 37Air Rate, 1b./hr 104. 3 85. 4 Ash In, lb./hr 1. O5 0. 79 Ash Collected,lb./hr 0.87 0.71 Ash Out, lb./hr O. 18 0.08 Ash Collection Efficiency ofFluidized Bed,

Percent 82. 7 90. 0 Ash Collection Efficieney of Bed and Cyclone,

Percent 97. 7 99. 0

Z It has also been found that certain additives can be mixed with'thecoal feed'to' promote the ash collection efiiciency in the combustionzone. For example the -addition of soda ash has been shown" to flux the:coal ash to forma lower meltingmixture. A uniform mixture of soda ash inthe coal feed'wasprepared by tumblingthe mixture-for 24 hours. A sodaash content of'2'.0 percent was used. Theash collection efiiciency ofthe bed was found to increase considerably over the range ofbedtemperature from about170 F. to about 1900 F. and higher.

Nonfluxing agents orinert diluents such as'silica can be used to permithigher temperature operation, when this is desirable, by retarding therate of agglomera tion.

What is claimed isz 1. A process for burning carbonaceous fuel" toproduce dust-free combustion gas which process comprises thev (e)withdrawing. essentially carbon-free agglomerated ash particles fromsaid combustion zone and' (f) withdrawingthe dust-free gas fromasaidcombustion zone. 2. The process of claim 1 wherein the bed temperaturein the combustion zone is-maintained at'about the=temperature ofincipient fusion of the ash produced from' burning said carbonaceousfuel. 7 o

3. A process for burning carbonaceous solid'particles to producedust-free combustion gas which process comprises the steps of:

(a) introducing said carbonaceous solid particles into a combustionzone, 7 1 (b) burning said carbonaceous solid particles with airinstantly as they are introduced into said com bustion zone, (-0)maintaining in said combustion zone a bed of fluidized ash particleswhich are produced from'the.

combustion of said carbonaceous solid particles, (d) controlling the bedtemperature in said combustion zone so as to cause the ash particles tobecome tacky and to agglomerate, (e) withdrawing'essentially carbon-freeagglomerated ash particles from said combustion zone, and I (f)withdrawing the dust-free gas from said combustion zone. 4. The processof claim 3 wherein said carbonaceous solid particles are pulverizedcoal. I

5. The process ofclaim 4 wherein the .bed temperature in said combustionzone isfroin about 1900. F. to about 2100 F. 5 6. The process of claim 3wherein the bedv temperature is maintained at about the incipient fusiontemperature of the ash particles produced. during the combustionreaction.

7. The process of claim 3 wherein solid particles are introduced intosaid combustion zone as a slurry of said carbonaceous solid particles inwater.

8. The process of claim B'Wherein water is introduced separately intothe comb st on zone.

the carbonaceous 9. The process of claim 3 wherein a fluxing agent isadded-to said carbonaceous solid particles.

10. The process-of claim 3 wherein the hot agglomerated ash particleswithdrawn from said combustion zone are utilized as heat-supply sourceand-to effect temperature control in the combustion zone.

11. A process for burning and gasifying carbonaceous solid particles intwo separate and inter-connected zones, which process comprises thesteps of (a) introducing carbonaceous solid particles into a combustionzone, 7

(b) burning said carbonaceous-solid particles with air instantly upontheir introduction into said combustion zone,

(0) maintaining in said combustion zone a bed of fluidized ashparticleswhich areproduced from the combustion of said carbonaceous solidparticles,

(d) controlling the-bed temperature in said combustion zone so as tocause the ash particles to become tacky and to agglomerate,

(e) withdrawing an essentially carbon-free heated agglomerated ash fromsaid combustion zone and conveying same into a gasification zone,

(f) withdrawing the dust-free .gas from said combustion zone,

(g) introducing carbonaceous solid particles and steam into saidgasification zone and supporting said carbonaceous solid particles influidized conditions in said gasification zone by means'of theintroduced steam,

(h) causing said heated agglomerated ash particles to descend in saidgasification zone and transferring the sensible heat of said heatedagglomerated ash particles to the fluidized bed'carbonaceous particlesand to thesteam in said, gasification zone to thereby supply the beatrequired to efiect a gasification reaction,

(i) removing. the gasesproduced in the gasification zone therefrom, and

(j) withdrawing agglomerated ash particles from said gasification zone.

, 12. The process of claim 11 wherein said carbonaceous solid particlesare pulverized coal.

13. The process of claim 11 wherein said carbonaceous solid particlesareintroduced as a slurry of carbonaceous solid particles in water.

14. Theprocess of claim 11 wherein water is introduced separately intosaid combustion zone.

15. The process of claim 11 wherein the temperature in the combustionzone is maintained at about the incipient fusion temperature of the ashparticles produced during the combustion reaction.

16'. The process of claim 11 wherein the temperature in the combustionzone is from about 1900 F. to about 2100 F. andthe temperature in thegasification zone is from about 1500" F. to 1700 F.

17. The process of claim 11 wherein the carbonaceous solid particlesfrom the gasification zone are recycled to the combustion zone.

References Cited by the Examiner UNITED STATES PATENTS 2,357,303 9/44Kerr et al 1l028 2,729,428 l/ 5 6 Milmore 28 2,741,549 4/56 Russell110-28 2,868,631 1/59 Woebcke -Q 48-206 2,958,298 11/60 Mayers 1l0,28

JAMES W. WESTHAVER, Primary Examiner. FREDERICK L. MATTESON, JR.,Examiner.

1. A PROCESS FOR BURNING CARBONACEOUS FUEL TO PRODUCE DUST-FREECOMBUSTION GAS WHICH PROCESS COMPRIES THE STEPS OF: (A) INTRODUCING SAIDCARBONACEOUS FUEL INTO A COMBUTION ZONE, (B) BURNING SAID CARBONACEOUSFUEL WITH AIR INSTANTLY AS SAID FUEL ENTERS THE COMBUSTION ZONE, (C)MAINTAINING IN SAID COMBUSTION ZONE A BED OF FLUIDIZED ASH PARTICLESWHICH ARE PRODUCED FROM THE (D) CONTROLLING THE BED TEMPERATURE IN SAIDCOMBUSTION ZONE AS TO CAUSE THE ASH PARTICLES TO BECOME TACKY AND TOAGGLOMERATE, (E) WITHDRAWING ESSENTIALLY CARBON-FREE AGGLOMERATED ASHPARTICLES FROM SAID COMBUSTION ZONE, AND (F) WITHDRAWING THE DUST-FREEGAS FROM SAID COMBUSTION ZONE.